During the past year I have continued investigations on the normal and abnormal development of visual cells in rabbit visual system, and on its detailed organizational plan. Included in the first group of studies is the finding that unilateral eyelid suturing would delay the development of striate cortical cells having oriented receptive fields, but that these cells eventually recovered to reach the normal state. Such deprivation procedure also affected the normal development of oriented cells in the lateral geniculate body and superior colliculus. Questions regarding whether long-term visual deprivation would permanently damage these cells and whether a critical period exists are under investigation. Current studies related to the second research area include the following: (1) We have described the receptive field characteristics of cells in the rabbit temporal cortex responding to visual stimulation, an area well outside the traditionally defined visual areas. Its afferent and efferent connections are demonstrated by several histological methods. (2) Using the horseradish peroxidase labelling technique, the retinal and cortical afferent systems to either the lateral geniculate body or the superior colliculus are studied. (3) Unit or unit-cluster recordings along the microelectrode tract tangential to the cortical surface indicated that the rabbit striate cortex is organized into columns, 0.5 mm apart, representing spatial subdivisions of the visual field. There is, however, extensive overlapping and mixing of receptive field types within each column. BIBLIOGRAPHIC REFERENCES: Grobstein, P. and Chow, K.L. Receptive field development and individual experience. Science 190: 352-358, 1975. Grobstein, P. and Chow, K.L. Receptive field organization in the mammalian visual cortex: the role of individual experience in development. Studies on the Development of Behavior and the Nervous System, Vol. 3, pp. 155-193, 1976.